This invention relates generally to nuclear reactors and more particularly, to apparatus and methods for coupling piping within reactor pressure vessels of such reactors.
A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends, e.g., by a bottom head and a removable top head. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure.
Boiling water reactors have numerous piping systems, and such piping systems are utilized, for example, to transport water throughout the RPV. For example, core spray piping is used to deliver water from outside the RPV to core spray spargers inside the RPV. The core spray piping and spargers deliver water flow to the reactor core.
Stress corrosion cracking (SCC) is a known phenomenon occurring in reactor components, such as structural members, piping, fasteners, and welds, exposed to high temperature water. The reactor components are subject to a variety of stresses associated with, for example, differences in thermal expansion, the operating pressure needed for the containment of the reactor cooling water, and other sources such as residual stresses from welding, cold working and other inhomogeneous metal treatments. In addition, water chemistry, welding, heat treatment and radiation can increase the susceptibility of metal in a component to SCC.
Reactor internal piping, such as T-boxes and core spray line downcommers, occasionally require replacement as a result of SCC. Replacing the core spray piping often requires removing and replacing the core spray line downcommer. The core spray line downcommer attachment to the shroud, however, typically is installed during original reactor construction and is difficult to access. In addition, replacing the core spray line downcommer is complicated by the limited available working space.
The core spray line downcommer includes a lower elbow secured to a shroud core spray sparger T-box. Installing a replacement downcommer pipe into the reactor requires that the replacement lower elbow be welded to the shroud. However, as explained above, it is difficult to access this area of the reactor.
It would be desirable to provide an apparatus which facilitates replacing a core spray line downcommer attached to the shroud core spray sparger T-box. It would also be desirable to provide such an apparatus which is installed without the necessity of field welding.